Bio-efficacy of a native strain of entomopathogenic nematode, <i>Steinernema siamkayai</i> against fall armyworm, <i>Spodoptera frugiperda</i> (J.E. Smith) (Lepidoptera: Noctuidae)

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The fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is a serious pest known for its ability to feed on various crops, particularly maize, inflicting significant reduction in maize yield. Farmers have traditionally dependent on chemical insecticides to manage this pest. These insecticides are frequently ineffective because the pest’s hidden feeding habits hinder the chemicals from reaching their intended target. In response to this challenge, an in vitro bioassay was performed to evaluate the virulence of an entomopathogenic nematode Steinernema siamkayai against third-instar larvae of Spodoptera frugiperda and wax moth (Galleria mellonella) at different concentrations of infective juveniles. Mortality rates were monitored from 24 to 96 h post-inoculation, with S. siamkayai demonstrating notable effectiveness against both insect species. For the fall armyworm, mortality rates risen progressively, beginning at 16.66% for 100 IJs larva-1 after 24 h, reaching 83.33% at 48 h, and achieving 100% by 96 h for doses of 30 IJs larva-1 or more. Wax moth larvae, on the other hand, showed greater susceptibility, with 22.91% mortality at 5 IJs larva-1 within 24 h and 100% mortality at 100 IJs larva-1 by the 48-hour mark. After 96 h, complete mortality was recorded in both species at doses of 30 IJs larva-1 or higher. Probit analysis indicated lower LC50 values for G. mellonella (1.83 and 0.87 IJs larva-1 at 72 and 96 h) compared to FAW (9.83 and 5.47 IJs larva-1). These findings suggest that S. siamkayai is a highly efficient bio-control agent, especially for managing S. frugiperda, and shows potential for integration into pest management programs.